Radiographic images such as X-ray photographic images are generally employed for medical diagnoses. To obtain X-ray photographic images is generally employed conventional X-ray photography. Thus, X-rays, having passed through a photographic object, are allowed to be irradiated onto a phosphor layer (fluorescent screen) to produce visible light, and the visible light produced is irradiated onto a conventionally used silver salt film, which is further developed to obtain the images. Recently, there is known a method of taking out images directly form a phosphor layer without the use of the silver salt film. The radiation, having passed through an object, is allowed to be absorbed in the phosphor, then the phosphor is excited by light or heat energy to release the radiation energy stored in the phosphor as fluorescence, and the resulting fluorescence is detected to form images. Exemplarily, there is known a radiation image conversion method using a stimulable phosphor, as disclosed in U.S. Pat. No. 3,859,527 and JP-A 55-12144 (hereinafter, the term, JP-A means a Unexamined and Published Japanese Patent Application).
In the method, a radiation image conversion panel (in other words, an image storage phosphor sheet) comprising a stimulable phosphor is employed, and the method comprises the steps of causing the stimulable phosphor of the panel to absorb radiation which passed through an object or having radiated from an object, sequentially exciting the stimulable phosphor with a electromagnetic waves such as visible light or infrared rays (hereinafter referred to as "stimulating rays") to release the radiation energy stored in the phosphor as light emission (stimulated emission), photoelectrically detecting the emitted light to obtain electrical signals, and reproducing the radiation image of the object as a visible image from the electrical signals.
In the radiation image recording and reproducing methods described above, a radiation image is advantageously obtained with a sufficient amount of information by applying radiation to an object in a considerably smaller dose, as compared to conventional radiography employing a combination of a radiographic film and a radiographic intensifying screen.
The stimulable phosphor, after being exposed to radiation, exhibits stimulated emission upon exposure to the stimulating ray. In practical use, phosphors are employed, which exhibit an emission within a wavelength region of 300 to 500 nm stimulated by stimulating light at wavelengths of 400 to 900 nm.
Examples of the stimulable phosphor used in the radiation image conversion panel include,
(1) a rare earth activated alkaline earth metal fluorohalide phosphor represented by the formula of (Ba.sub.1-x,M.sup.2+.sub.x)FX:yA, as described in JP-A 55-12145, in which M.sup.2+ is at least one of Mg, Ca, Sr, Zn and Cd; X is at least one of Cl, Br and I; A is at least one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, and Er; x and y are numbers meeting the conditions of 0.ltoreq.x.ltoreq.0.6 and 0.ltoreq.y.ltoreq.0.2; and the phosphor may contain the following additives: PA1 (2) a divalent europium activated alkaline earth metal halide phosphor described in JP-A 60-84381, represented by the formula of M.sup.2 X.sub.2.aM.sup.2 '.sub.2 :xEu.sup.2+ (in which M.sup.2 is an alkaline earth metal selected from the group of Ba, Sr and Ca; X and X' is a halogen atom selected from the group of Cl, Br and I and X.noteq.X'; a and x are respectively numbers meeting the requirements of 0.ltoreq.a.ltoreq.0.1 and 0.ltoreq.x.ltoreq.0.2); PA1 (3) a rare earth element activated rare earth oxyhalide phosphor represented by the formula of LnOX:xA, as described in JP-A 55-12144 (in which Ln is at least one of La, Y, Gd and Lu; A is at least one of Ce and Tb; and x is a number meeting the following condition, 0&lt;x&lt;0.1); PA1 (4) a cerium activated trivalent metal oxyhalide phosphor represented by the formula of M.sup.3 OX:xCe, as described in JP-A 58-69281 (in which M.sup.3 is an oxidized metal selected from the group of Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Bi; X is a halogen atom selected from the group of Cl, Br and I; x is a number meeting the following condition, 0&lt;x&lt;0.1; PA1 (5) a bismuth activated alkali metal halide phosphor represented by the formula of M.sup.1 X:xBi, as described in Japanese Patent Application No.60-70484 (in which M.sup.1 is an alkali metal selected from the group of Rb and Cs; X is a halogen atom selected from the group of Cl, Br and I; x is a number meeting the following condition, 0&lt;x.ltoreq.0.2; PA1 (6) a divalent europium activated alkaline earth metal halophosphate phosphor represented by the formula of M.sup.2.sub.5 (PO.sub.4).sub.3 X:xEu.sup.2+, as described in JP-A 60-141783 (in which M.sup.2 is an alkaline earth metal selected from the group of Ca, Sr and Ba; X is a halogen atom selected from the group of F, Cl, Br and I; x is a number meeting the following condition, 0&lt;x.ltoreq.0.2); PA1 (7) a divalent europium activated alkaline earth metal haloborate phosphor represented by the formula of M.sup.2.sub.2 BO.sub.3 X:xEu.sup.2+, as described in JP-A 60 157099 (in which M.sup.2 is an alkaline earth metal selected from the group of Ca, Sr and Ba; X is a halogen atom selected from the group of Cl, Br and I; x is a number meeting the following condition, 0&lt;x.ltoreq.0.2); PA1 (8) a divalent europium activated alkaline earth metal halophosphate phosphor represented by the formula of M.sup.2.sub.2 PO.sub.4 X:xEu.sup.2+, as described in JP-A 60-157100 (in which M.sup.2 is an alkaline earth metal selected from the group of Ca, Sr and Ba; X is a halogen atom selected from the group of Cl, Br and I; x is a number meeting the following condition, 0&lt;x.ltoreq.0.2); PA1 (9) a divalent europium activated alkaline earth metal hydrogenated halide phosphor represented by the formula of M.sup.2 HX:xEu.sup.2+, as described in JP-A 60-217354 (in which M.sup.2 is an alkaline earth metal selected from the group of Ca, Sr and Ba; X is a halogen atom selected from the group of Cl, Br and I; x is a number meeting the following condition, 0&lt;x.ltoreq.0.2); PA1 (10) a cerium activated rare earth complex halide phosphor represented by the formula of LnX.sub.3.aLn'X.sub.3 ':xCe.sup.3+, as described in JP-A 61-21173 (in which Ln and Ln' are respectively a rare earth element selected from the group of Y, La, Gd and Lu; X and X' are respectively a halogen atom selected from the group of F, Cl, Br and I and X.noteq.X'; a and x are respectively numbers meeting the following conditions, 0.1&lt;a.ltoreq.10.0 and 0&lt;x.ltoreq.0.2; PA1 (11) a cerium activated rare earth complex halide phosphor represented by the formula of LnX.sub.3.aM.sup.1 X':xCe.sup.3+, as described in JP-A 61-21182 (in which Ln and Ln' are respectively a rare earth element selected from the group of Y, La, Gd and Lu; M.sup.1 is an alkali metal selected from the group of Li, Na, k, Cs and Rb; X and X' are respectively a halogen atom selected from the group of Cl, Br and I; a and x are respectively numbers meeting the following conditions, 0.1&lt;a.ltoreq.10.0 and 0&lt;x.ltoreq.0.2; PA1 (12) a cerium activated rare earth halophosphate phosphor represented by the formula of LnPO.sub.4.aLnX.sub.3 :xCe.sup.3+, as described in JP-A 61-40390 (in which Ln is a rare earth element selected from the group of Y, La, Gd and Lu; X is a halogen atom selected from the group of F, Cl, Br and I; a and x are respectively numbers meeting the following conditions, 0.1&lt;a.ltoreq.10.0 and 0&lt;x.ltoreq.0.2; PA1 (13) a divalent europium activated cesium rubidium halide phosphor represented by the formula of CsX:aRbX':xEuM.sup.2+, as described in Japanese Patent Application No. 60-78151 (in which X and X' are respectively a halogen atom selected from the group of Cl, Br and I; a and x are respectively numbers meeting the following conditions, 0.1&lt;a.ltoreq.10.0 and 0&lt;x.ltoreq.0.2; PA1 (14) a divalent europium activated complex halide phosphor represented by the formula of M.sup.2 X.sub.2.aM.sup.1 X':xEu.sup.2+, as described in Japanese Patent Application No.60-78153 (in which M.sup.2 is an alkaline earth metal selected from the group of Ba, Sr and Ca; M.sup.1 is an alkali metal selected from the group of Li, Rb and Cs; X and X' are respectively a halogen atom selected from the group of Cl, Br and I; a and x are respectively numbers meeting the following conditions, 0.1&lt;a.ltoreq.20.0 and 0&lt;x.ltoreq.0.2. PA1 (1) forming a stimulable phosphor and PA1 (2) coating the formed stimulable phosphor with particles of a metal oxide, and a silane coupling agent or a metal alkoxide; PA1 (1) forming a stimulable phosphor precursor, PA1 (2) calcining the formed precursor in the presence of particles of a first metal oxide, and PA1 (3) coating the calcined precursor with a silane coupling agent or metal alkoxide; PA1 (1) forming a stimulable phosphor precursor, PA1 (2) calcining the formed precursor in the presence of a metal alkoxide, and PA1 (3) coating the calcined precursor with a silane coupling agent or metal alkoxide, and particles of a metal oxide; PA1 (1) forming a stimulable phosphor precursor, PA1 (2) calcining the formed precursor in the presence of a first metal alkoxide and particles of a first metal oxide, and PA1 (3) coating the calcined precursor with a silane coupling agent or a second metal alkoxide; PA1 forming a phosphor layer containing a stimulable phosphor prepared according to the method as described in 1; PA1 forming a phosphor layer containing a stimulable phosphor prepared according to the method as described in above 9. PA1 forming a phosphor layer containing a stimulable phosphor prepared according to the method as described in above 19; PA1 forming a phosphor layer containing a stimulable phosphor prepared according to the method as described in above 22. PA1 coating particles of the stimulable phosphor with particles of a metal oxide and PA1 subjecting the particles of the stimulable phosphor to surface treatment using a silane coupling agent; PA1 calcining precursor particles of the rare earth activated alkaline earth metal fluoroiodide stimulable phosphor in the presence of first metal oxide particles with a particle size of 2 to 50 nm and then coating the calcined particles with a silane coupling agent, or PA1 calcining the precursor particles in the presence of the metal oxide and then coating the calcined particles with second metal oxide particles with a particle size of 2 to 50 nm and a silane coupling agent; PA1 calcining precursor particles of the rare earth activated alkaline earth metal fluoroiodide stimulable phosphor in the presence of first metal oxide particles with a particle size of 2 to 50 nm and then coating the calcined particle surface with a metal alkoxide of at least one of aluminum, zirconium, titanium, silicon and barium, or PA1 calcining the precursor particles in the presence of the metal oxide and then coating the calcined particle surface with second metal oxide particles with a particle size of 2 to 50 nm and a metal alkoxide of at least one of aluminum, zirconium, titanium, silicon and barium; PA1 precursor particles of the stimulable phosphor, a first metal oxide particles coated on the precursor particle surface, and PA1 a metal alkoxide of at least one of aluminum, zirconium, titanium, silicon and barium which is, after calcination, coated on the stimulable phosphor, or the metal alkoxide and second metal oxide particles; PA1 preparing within a reaction vessel an aqueous mother liquor containing at least 1 mol/l (preferably at least 1.35 mol/l and more preferably 3.0 to 4.5 mol/l) BaX.sub.2 (BaI.sub.2, BaBr.sub.2 except for a fluoride) and a halide of Ln, provided that when x of the formula (1) is not zero, the mother liquor further contains a halide of M.sup.1 and when y is not zero, the mother liquor further contains a halide of M.sup.2, PA1 adding an aqueous solution containing a at least 5 mol/l (preferably, at least 8 mol/l and more preferably 10 to 13 mol/l) inorganic fluoride (preferably, ammonium fluoride or alkaline metal fluoride) into the mother liquor, while maintaining the mother liquor at 50.degree. C. or more (preferably, 80.degree. C. or more) to form a crystalline precipitate of a precursor of the rare earth activated alkaline earth metal fluoroiodide stimulable phosphor, PA1 separating the crystalline precipitate of the precursor from the mother liquor, and PA1 calcining the separated precipitate while avoiding sintering of the precipitate, to form the stimulable phosphor. Herein, the expression, "avoiding sintering of the precipitate" means to avoid fusing of precipitated particles of the phosphor precursor during calcination. PA1 (a) preparing within a reaction vessel an aqueous mother liquor containing an at least 3 mol/l (preferably, at least 4 mol/l) BaX.sub.2 (BaI.sub.2, BaBr.sub.2 except for a fluoride) and a halide of Ln, provided that when x of the formula (1) is not zero, the mother liquor further contains a halide of M.sup.1 and when y is not zero, the mother liquor further contains a halide of M.sup.2, PA1 (b) adding continuously or intermittently an aqueous solution containing an at least 5 mol/l (preferably at least 8 mol/l, and more preferably 10 to 13 mol/l) inorganic fluoride (preferably, ammonium fluoride or alkaline metal fluoride) and an aqueous solution containing BaI.sub.2 to the mother liquor, while maintaining a temperature of at least 50.degree. C. (preferably, at least 80.degree. C.) and keeping constant a molar ratio of fluorine of the fluoride solution to barium of the BaI.sub.2 solution, to form a crystalline precipitate of a precursor of the rare earth activated alkaline earth metal fluoroiodide stimulable phosphor, PA1 (c) separating the precipitate of the precursor from the mother liquor, and PA1 (d) calcining the separated precipitate while avoiding sintering of the precipitate. PA1 1. a radiation image conversion panel comprising a phosphor sheet having a stimulable phosphor layer provided on a support and a moisture-proofing film provided thereon so as to cover the phosphor layer side of the phosphor sheet, wherein the moisture-proofing film is a laminated film in which plural resin films including a metal oxide-deposited resin film are layeredly adhered, the laminated film having plural adhesive layers and the adhesive layers not containing a hardenable adhesive layer with a thickness of not more than 2.5 .mu.m; PA1 2. the radiation image conversion panel described in 1 above, wherein the outermost resin layer of the moisture-proofing film of the side in contact with the phosphor sheet is comprised of a heat-adhesive resin, the heat-adhesive resin layer containing 0.01 to 1.0% by weight of fine inorganic particles; and PA1 3. the radiation image conversion panel described in 1 or 2 above, wherein the moisture-proofing film is provided on the upper and lower sides of the phosphor sheet so that the moisture-proofing film coats the entire surface of the phosphor sheet and is substantially not adhered to the phosphor layer, the periphery of the moisture-proofing film being set outside the periphery of the phosphor sheet, and that a moisture-proofing film on the support-side is one which is laminated with an aluminum film.
X', BeX" and M.sup.3 X.sub.3 '", as described in JP-A 56-74175 (in which X', X" and X'" are respectively a halogen atom selected from the group of CL, Br and I; and M.sup.3 is a trivalent metal); PA2 a metal oxide described in JP-A 55-160078, such as BeO, BgO, CaO, SrO, BaO, ZnO, Al.sub.2 O.sub.3, Y.sub.2 O.sub.3, La.sub.2 O.sub.3, In.sub.2 O.sub.3, SiO.sub.2, TiO.sub.2, ZrO.sub.2, GeO.sub.2, SnO.sub.2, Nb.sub.2 O.sub.5 or ThO.sub.2 ; PA2 Zr and Sc described in JP-A 56-116777; PA2 B described in JP-A 57-23673; As and Si described in JPA 57-23675; PA2 M.L (in which M is an alkali metal selected from the group of Li, Na, K, Rb and Cs; L is a trivalent metal Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga, In, and Tl) described in JP-A 58-206678; PA2 calcined tetrafluoroboric acid compound described in JPA 59-27980; PA2 calcined, univalent or divalent metal salt of hexafluorosilic acid, hexafluorotitanic acid or hexafluorozirconic acid described in JP-A 59-27289; PA2 NaX' described in JP-A 59-56479 (in which X' is at least one of Cl, Br and I); PA2 a transition metal such as V, Cr, Mn, Fe, Co or Ni, as described in JP-A 59-56479; PA2 M.sup.1 X', M'.sup.2 X", M.sup.3 X'" and A, as described in JP-A 59-75200 (in which M.sup.1 is an alkali metal selected from the group of Li, Na, K, Rb and Cs; M'.sup.2 is a divalent metal selected from the group of Be and Mg; M.sup.3 is a trivalent metal selected from the group Al, Ga, In and Tl; A is a metal oxide; X', X" and X'" are respectively a halogen atom selected from the group of F, Cl, Br and I);M.sup.1 X' described in JP-A 60-101173 (in which M.sup.1 is an alkali metal selected from the group of Rb and Cs; and X' is a halogen atom selected from the group of F, Cl, Br and I); PA2 M.sup.2 'X'.sub.2.M.sup.2 'X".sub.2 (in which M.sup.2 ' is at least an alkaline earth metal selected from the group Ba, Sr and Ca; X' and X" are respectively a halogen atom selected from the group of Cl, Br and I, and X'.noteq.X"); and PA2 LnX".sub.3 described in Japanese Patent Application No. 60106752 (in which Ln is a rare earth selected from the group of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; X" is a halogen atom selected from the group of F, Cl, Br and I); PA2 the phosphor may contain the following additives; PA2 M.sup.1 X" described in JP-A 60-166379 (in which M.sup.1 is an alkali metal selected from the group of Rb, and Cs; X" is a halogen atom selected from the group of F, Cl, Br and I; PA2 KX", MgX.sub.2 '" and M.sup.3 X.sub.3 "" described in JP-A 221483 (in which M.sup.3 is a trivalent metal selected from the group of Sc, Y, La Gd and Lu; X", X'" and X"" are respectively a halogen atom selected from the group of F, Cl Br and I; PA2 B described in JP-A 60-228592; PA2 an oxide such as SiO.sub.2 or P.sub.2 O.sub.5 described in JP-A 60-228593; PA2 LiX" and NaX" (in which X" is a halogen atom selected from the group of F, Cl, Br and I; PA2 SiO described in JP-A 61-120883; PA2 SnX.sub.2 " described in JP-A 61-120885 (in which X" is a halogen atom selected from the group of F, Cl, Br and I; PA2 CsX" and SnX.sub.2 '" described in JP-A 61-235486 (in which X" and X'" are respectively a halogen atom selected from the group of F, Cl, Br and I; PA2 CsX" and Ln.sup.3+ described in JP-A 61-235487 (in which X" is a halogen atom selected from the group of F, Cl, Br and I; Ln is a rare earth element selected from the group of Sc, Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu;
Of stimulable phosphors above-described, an iodide-containing divalent europium activated alkaline earth metal fluorohalide phosphor, an iodide-containing divalent europium activated alkaline earth metal halide phosphor, an iodide containing rare earth element activated rare earth oxyhalide phosphor and an iodide-containing bismuth activated alkaline metal halide phosphor each exhibit stimulated emission with high luminance.
The radiation image conversion panel using a stimulable phosphor, after storage of radiation image information, releases stored energy by scanning the panel with stimulating light so that after scanning, radiation images can again be stored. Thus, the radiation image conversion panel can be used repeatedly. In the conventional radiography, a sheet of the radiographic film is consumed for each photograph; on the other hand, this radiation image converting method, in which the radiation image conversion panel is employed repeatedly, is also advantageous in terms of conservation of resources and economical efficiency.
Accordingly, there is desired a radiation image conversion panel capable of use over a long period of time without deteriorating.
However, stimulable phosphors used in the radiation image conversion panel generally have a marked tendency of moisture sorption. When allowed to stand under ordinary climatic conditions, the stimulable phosphor absorbs atmospheric moisture and markedly deteriorates over elapsed time.
When allowed to stand under high humidity, for example, sensitivity to radiation of the stimulable phosphor is lowered with an increase of adsorbed moisture. Latent images of radiation images recorded in the stimulable phosphor generally fade over time after exposure to radiation, exhibiting the tendency that the longer the time between exposure to radiation and scanning with stimulating light, the smaller the reproduced radiation image signal intensity. Thus, moisture sorption of the stimulable phosphor accelerates the latent image fading. The use of a radiation image conversion panel comprised of a moisture-sorbed stimulable phosphor leads to deteriorated reproduction of signals when reading radiation images.
To prevent stimulable phosphors from deterioration due to moisture sorption, there were proposed a method of reducing moisture reaching a stimulable phosphor layer by coating the phosphor layer with a moisture-resistant protective layer or moisture-resistant resin film, a method of using fine hydrophobic particles described in JP-B 62-177500 (hereinafter, the term, JP-B means a published Japanese Patent), a method of using silane coupling agents described in JP-B 62-209398, a method of using titanate type coupling agents described in JPB 2-278196, and a method of using silicone oil described in JP-B 5-52919. However, there has not yet been achieved a fundamental solution to the problems described above.
As is known, stimulabilty of a stimulable phosphor depends on its particle size, and JP-A 55-163500 teaches the preferred average particle size being 1 to 30 .mu.m. JP-B 3-79680 also discloses the relationship between the phosphor particle size and characteristic values such as sensitivity, graininess and sharpness. JP-A 7-233369 discloses a means to control the stimulable phosphor particle size and form ina liquid phase process. Thus, contrary to the conventional preparation of a rare earth activated alkaline earth metal fluorohalide stimulable phosphor, in which raw materials of an alkaline earth metal fluoride, an alkaline earth metal halide other than the fluoride, a rare earth halide and ammonium fluoride are mixed in a dry process or are mixed while being dispersed in an aqueous medium and thereafter are calcined and ground, the rare earth activated alkaline earth metal fluorohalide stimulable phosphor is precipitated in an aqueous solution. According the above liquid phase process of precipitating the rare earth activated alkaline earth metal fluorohalide stimulable phosphor in an aqueous solution was obtained fine phosphor particles with homogeneous size with no deterioration of performance. However, as sensitivity is enhanced and the particle size decreases, problems such as deterioration due to moisture becomes evident. The deterioration starts as soon as calcined phosphor particles are exposed to air. To prevent this, it is contemplated to store the calcined phosphor particles in an atmosphere shielded from air. However, it is impractical to conduct all of the process of preparing the phosphor plate in such an atmosphere.